Electrical apparatus



L. H. BEDFORD ETAL 2,360,466

ELECTRICAL APPARATUS Filed Aug. 20, 1941 GAIN Cour/e01.

VOL TA 6 E Patented Get. 17, lg

ELEGTBICAL APPARATUS Leslie Herbert Bedford and Walter Henry Stevens,London, England, assignors to A. C. Cossor Limited, London, England, a.company of England Application August 20, 1941, Serial No. 407,689 InGreat Britain May 27, 1940 of the suppressors are reduced abruptly bythe 8 Claims.

nal potential, the input being applied to the con-' trol grid of thefirst valve, and the screen of the second valve being coupled to theanode of the first valve to provide the output, the whole arrangementbeing such that the anode currents of both valves are cut oii whendesired by a reduction of the potentials of the suppressors, and theresulting increase of screen current of the second valve is substitutedfor the anode current of the first valve.

In the accompanying drawing, Fig. 1 illustrates the use of the.invention in a radio frequency amplifier stage, and Fig, 2 illustratesits application to the production of a polar diagram on the screen of acathode ray tube. Fig. '1 shows a circuit diagram of a radio frequencyamplifier stage in which the input signal is applied between earth andthe terminal I, which is connected tothe control grid of a pentodeamplifler valve V1.

The screen of pentode V1 is maintained at constant potential equal tothe mean anode potential, being connected to a high tension source andalso being connected through condenser C1 to earth.

A second pentode valve V2, having identical characteristics with valveVi, has its screen directly connected to the anode of valve V1. Itscontrol grid is directly'connected to earth. Valves V1, V2 are providedwith equal anode load resistors R1, R2 and equal self-biassing resistorsR3, R4 and by-pass condensers C2, C3 re spectively.

The suppressors of valves V1, V2 are directly connected together. It maybe necessary to insert a small resistance, the value of which may be ofthe order of 100 ohms, in the connection between the suppressors toprevent parasitic o'scillations.

During the transmission of signals, the potentials of the suppressorsare maintained constant, for example, at cathode potential. The screencurrent of valve V2, therefore, remains constant, and in flowing throughresistor R1 does not disturb the alternating component of the outputvoltage which is developed across resistor R1 and obtained betweenterminal 2 and earth.

When it is desired to quash abruptly, either wholly or partly, theamplifier gain, the potentials application of a negative potential toterminal 3.

A change of potential of the suppressor of a pentode valve does notappreciably afiect the cathode current; it merely changes the proportionin which the cathode current is divided between anode and screen. Thedecrease of anode current, therefore, appears as an increase of screencurrent.

The two valves V1, V2 are under substantially identical mean operatingconditions and they have substantially identical characteristics. Theincrease of screen current of valve V2 for a given reduction ofpotential of the suppressors is, therefore, equal to the correspondingdecrease of mean anode current of valve V1. It follows that the abruptreduction of the potentials of the suppressors does not lead toanychange in the direct component of current in anode load R1. Further, theabsence of elaboratei circuits between the valves results in theavoidance of time delay between the decrease of anode current of valveV1 and the increase of screen current of valve V2. Quashing of the gainof the amplifier is therefore efiected without producing spuriousoscillations of the kind known as ringing.

The invention may be applied to a television transmitter videoamplifier, for the purpose of substituting for the picture signal asignal of steady value. This may, for example, be a signal representingfull black, which is inserted at the end of the scanning of each line ofthe picture. The steady value required will not normally be equal to themean value of the picture signal. The increase of screen current onvalveVz for a given change of potential of the suppressors will,therefore, be required to be somewhat difierent from the dgcrease ofanode current on valve "tion to the production of a polar diagram on theTwo pairs of pentode valves are employed, each pair being connectedin acircuit such as that shown inFig. 1.

In order to produce rotation of the beam at constant angular velocity,sine wave potentials in quadrature are applied to the control grids ofthe first valves of each pair. The output of one pair is applied to thedeflection system for. one direction of deflection, and the output ofthe other pair to the other deflection system.

The operating conditions of the valves are adjusted so that the trace onthe cathode-ray tube screen is circular.

Radial deflection of the spot is obtained by variation of the potentialsof the suppressors of both pairs of valves simultaneously.

A circuit of the above type is shown in Fig. 2. A and 13 represent twocircuits each of which corresponds with the circuit shown in Fig. 1. Theinput terminals I and I and output terminal 2 of circuit A correspond tothe like-numbered parts of Fig. 1, and the corresponding terminals ofcircuit 3 are numbered ll, ll and 2| respectively. A sine-wavealternating source I! is connected between the terminal I and the earthterminal of circuitA, and also through a quadrature phase shiftingdevice It to the corresponding input terminal H and earth terminal ofcircuit B. 'The potential variation for the control electrodes orsuppressors is applied between the terminals 4, 5, terminal l beingconnected to the input terminals 3 and Ii and terminal 5 to the earthconnections of circuits A and B.

A suitable cathode ray tube is arranged for asymmetrical deflection,deflector plates 8 and 9 being connected toearth. The opposite plates 5and 1 are coupled to the output terminals 2 and 2| of circuits A and Brespectively through coupling condensers II and I 8|. The grid leaks I3and "I are provided to maintain the mean potentials of plates 8 and I atthe potentials of plates 8 and 8. a

Various other types of valves besides pentodes have also the qualitythat the variation of potential of one of the electrodes is eflectivemerely to decrease the current flowing to one electrode and to increasethe current flowing to another electrode. The term "valve of the pentodetype in this specification is intended to cover all other valves whichshare this quality. When used in context with this term, the termssuppressor," "screen and "anode are intended merely to indicate theelectrodes in respect of which this quality obtains, independently ofthe question whether they have also the other functions assogated withsuch electrodes in the ordinary pen- A hexode, for example, is a valveof the pen-,

tode type. In the hexode, variation of the potter/- tial of the thirdgrid efi'ects the transfer of output current between 1) the anode, and(2) \the 2nd and 4th grids which are connected together. In the heirode,the third grid is to be regarded as the "suppressor although it does notsuppress the passage of secondary electrons between the screen, whichhere consists of the 2nd and 4th grids, and the anode. v t

In a preferred arrangement according to the invention, the two valves ofthe pentode type are enclosed in a single envelope and have a commoncathode.

In some applications of the invention, it may be desired to avoid directcurrent connection of suitably selected for the purpose for which thecircuit is required.

We claim:

1. A thermionic valve circuit comprising in combination two valves eachhaving at least a cathode, a first control electrode for controlling theelectron current emitted by said cathode, first and second outputelectrodes and a second control electrode for controlling thedistribution of current between said output electrodes, the potentlalsof said first output electrode of the first valve and said first,control electrode of the second valve being maintained constant relativeto said cathodes, input means coupled to said first control electrode ofthe first valve, additional input means coupled to both of said secondcontrol electrodes, and output means coupled to said second outputelectrode of the first valve and to said first output electrode of thesecond valve.

2. A thermionic valve circuit as defined in claim 1, said second controlelectrodes being directly connected together.

3. A thermionic valve circuit as defined in claim 1, said second outputelectrode of the first valve and said first output electrode of saidsecond valve being directly connected together.

4. A thermionic valve circuit as defined in claim characteristics andmean operating conditions.

5. A thermionic valve circuit comprising in combination two valves ofthe pentode type each having a cathode, control grid, screen,suppressor, and anode, the potentials of the screen of the first valveand the control grid of the second valve being maintained constantrelative to said cathodes, said suppressors being connected together andsaid anode of the firstvalve and screen of the second valve beingconnected together, input means coupled to said control grid of thefirst valve, additional input means coupled to said suppressors, andoutput means coupled to said connected anode and screen. I 6. Incombination with a cathode ray tube of the type having asymmetricdeflection in two mutually perpendicular directions, two thermionicvalve circuits as defined in claim 1, each of said circuits having itsoutput coupled to said tube, means for applying sine wave potentials inquadrature to said first-named input means of said circuits to producerotation of the beam at constant angular velocity, and means forsimultane-' ously applying potentials to said second-named input meansoi said circuits to produce radial deflections.

'7. An electrical circuit comprising in combination means to produce afirst electron discharge stream, a signal input electrode and a pair oroutput electrodes therefor, load impedance means connected to one ofsaid output electrodes, a volume control electrode adapted to vary therelative distribution of electron space current upon said outputelectrodes, means to produce a second electron discharge stream, a pairof output electrodes therefor, a volume control electrode adapted tovary the relative distribution of electron space current upon said lastmentioned output electrodes, means for applying a signal controlpotential to said input electrode and for deriving output potential fromsaid load means, means for applying further control potential to bothsaid volume control electrodes, and further means to pass additionaloutput current from one of the output electrodes of said seconddischarge stream through said load impedance, whereby to aseonse 3 asignal output circuit connected to both said 10 output electrodes, meansincluding a further control electrode for each of said discharge streamsfor varying the steady discharge currents to said v output electrodes inan opposite sense in accordance with a control potential simultaneouslyapplied to said further control electrodes, whereby to maintain thesteady current'through said output circuit substantially constantindependently of said control potential.

LESLIE HERBERT BEDFORD. WALTER HENRY STEVENS.

